A) Field of the Invention
The present invention relates to an image pick-up device, and more particularly to an image pick-up device having a number of pixels disposed in a honeycomb configuration.
B) Description of the Related Art
After integration and mass production techniques for charge coupled devices (CCD) have been established, image pick-up apparatuses such as digital still cameras and digital video cameras are rapidly prevailing, these image pick-up apparatuses using CCD type solid state image pick-up devices as area image sensors.
In a CCD type solid state image pick-up device, a number of photoelectric conversion elements (pixels) are disposed in a matrix shape in a plurality of rows and columns on the principal surface of a semiconductor substrate. A vertical CCD (VCCD) made of CCD is disposed along each pixel row. A horizontal CCD (HCCD) made of CCD is disposed connected to each output terminal of these VCCD's.
In a single plate type color CCD solid state image pick-up device, a color filter array is disposed above a number of pixels disposed in a matrix shape. The color filter array is made of color filters disposed above pixels. There are a color filter array of three primary colors and a color filter array of complementary colors. The color filter array of complementary colors includes an array made of only complementary color filters and an array made of complementary color filters and green color filters. The color filter produces the color of a pixel. If necessary, micro lenses are disposed on color filters.
As light becomes incident upon a pixel, charges corresponding in amount to the incident light are accumulated in the pixel. Charges accumulated in each pixel are read to VCCD and transferred to HCCD via VCCD's. Charges accumulated in pixels of one pixel row are read at the same timing into corresponding VCCD's and transferred at the same timing to the HCCD. HCCD sequentially transfers charges received from VCCD's toward an output terminal.
Charges output from HCCD are detected by an output circuit. The output circuit generates a voltage signal corresponding to the detected charges, amplifies the voltage signal and outputs it. The charges detected by the output circuit are drained, for example, to the drain region and then absorbed in a supply voltage. An image pick-up apparatus utilizing a CCD solid state type image pick-up device generates an image signal from the voltage signal (pixel signal: signal unit) output from the output circuit.
A conventional CCD solid state image pick-up device utilized as an area image sensor has a number of pixels disposed in a square matrix shape (or a matrix shape having different numbers of rows and columns).
Many recent CCD solid state image pick-up devices of high resolution and sensitivity have a honeycomb configuration which is easy to dispose pixels at a high integration and with a broader light reception area.
The term “honeycomb configuration” used in this specification means a configuration comprising a first lattice in a two-dimensional tetragonal matrix configuration and a second lattice having its lattice points at the interstitial position of the first lattice. For example, each pixel in an even pixel column (row) is shifted by about a half of the pitch of pixels in the column (row) direction from each pixel in an odd pixel column (row), and each pixel column (row) includes only pixels in odd rows (columns) or even rows (columns). The honeycomb configuration is one type of the configuration that a number of pixels are disposed in a matrix shape in a plurality of rows and columns.
The term “about a half” of the pitch is intended to include just a half and another value considered as substantially equal to a half from the CCD image sensor performance and image quality although this value is not correctly a half because of manufacture errors and pixel position rounding errors caused by design or mask.
If a subject is too dark, a sufficient image pick-up sensitivity cannot be obtained. If the subject is at a near position, a sufficient image pick-up sensitivity can be obtained by utilizing an electronic flash such as a strobe. However, if the subject is at a far position, a sufficient image pick-up sensitivity cannot be obtained even if an electronic flash is utilized.
The sensitivity of an image pick-up device can be increased by adding charges read from a plurality of pixels before amplification. In this specification, adding charges read from a plurality of pixels is called “pixel addition” where appropriate.
For example, luminance information can be obtained from pixel signals of two red pixels, two blue pixels and three green pixels. Information (color signal information) necessary for generating one color signal can be obtained from pixel signals of one red pixel and two green pixels. Color signal information can also be obtained from pixel signals of one blue pixel and two green pixels.
If the sensitivity of a single plate solid state image pick-up device with a color filter array of three primary colors is increased by pixel addition, the luminance may be lowered so that the resolution lowers, or the color signals may be lowered so that a false color is formed or a color S/N ratio lowers.
The sensitivity and resolution of an image pick-up device having a number of pixels disposed in a square matrix shape can be improved more by using a color filter array of complementary colors than by using a color filter array of three primary colors.
An image pick-up device having a number of complementary color pixels disposed in the honeycomb configuration is still not known which is easy to suppress reduction of a resolution, generation of a false color and reduction of a color S/N ratio even if the sensitivity is increased by pixel addition.